1 Field of the Invention
The present invention relates to a process for removing ink from wastepaper in order to provide paper pulp that may be reused to manufacture new paper. In particular, the invention is directed to a process for removing both water-based and oil-based inks from wastepaper by means of a novel group of deinking agents.
2. Description of the Prior Art
Recycled wastepaper has traditionally been a source of raw fiber materials needed in the papermaking industry. In the past, fiber from wastepaper was only employed in the production of low grade paper and paperboard products. Today, however, reclaimed fiber comprises about 25 percent of the total fiber used to manufacture paper, thereby providing an incentive for improving the utility of reclaimed paper pulp materials. In particular, recent efforts have attempted to develop techniques for effectively removing ink from waste fibers, in order to permit their use in the manufacture of high quality paper.
In conventional paper reclamation processes, deinking is carried out by converting the wastepaper to pulp and contacting the pulp with an alkaline aqueous deinking medium containing a chemical deinking agent, in order to remove ink and other impurities from the pulp fiber and produce a suspension or dispersion of the ink and other particles in the aqueous medium. The resulting mixture is subsequently treated to separate the suspended ink and other particles from the pulp, for example, by air sparging and floatation of the ink/deinking agent complex, followed by skimming to remove the ink and other particles from the treatment bath, or by filtration and subsequent water washing of the fiber mat to remove dispersed ink particles.
There have been numerous attempts in the prior art to improve the efficacy of conventional deinking processes. For example, U.S. Pat. No. 4,618,400 discloses a method for deinking wastepaper which involves converting the wastepaper to a pulp; contacting the pulp with an aqueous medium of alkaline pH containing about 0.2 to 2% by weight of a deinking agent which is one or a mixture of certain thiol ethoxylate compounds; and removing suspended or dispersed ink from the pulp-containing medium.
U.S. Pat. No. 4,666,558 illustrates a deinking process for waste newsprint, which involves contacting and agitating a pulped newsprint in an aqueous medium containing a deinking agent comprising a particular mixture of a water-soluble C.sub.9 to C.sub.16 alkanol ethoxylate component having an average of about 6.5 to 20 oxyethylene units per ethoxylate molecule and an oil-soluble C.sub.9 to C.sub.16 alkanol ethoxylate component having an average of about 0.5 to 3.5 oxyethylene units per ethoxylate molecule, and recovering deinked pulp from the aqueous medium.
U.S. Pat. No. 3,932,206 describes deinking agents which are said to be biodegradable and non-toxic to aquatic life; the disclosed compounds consist of ethoxylated aliphatic mono-or diols having from 14 to 30 carbon atoms in the aliphatic chain, and from 8 to 24 ethyleneoxy units per mole of the mono- or diol.
Despite the foregoing efforts, it is generally agreed that no completely acceptable process for deinking wastepaper presently exists. One shortcoming of many of the prior art deinking techniques is the inability of these processes to simultaneously remove both water-based and oil-based inks from the wastepaper. In this regard, substantial costs are associated with processing wastepaper materials to separate water-based ink containing materials from those which contain oil-based inks. Moreover, deinking agents utilized to date have bee ineffective in removing tacky contaminants from wastepaper. These tacky contaminants (from pressure sensitive labels, binding materials and glues) are frequently encountered in wastepaper deinking processes, and tend to limit the quality of the final recycled product.
It would therefore be highly desirable to provide a process for deinking various types of wastepaper which contain water-based and/or oil-based inks. In addition, it would be advantageous if such a deinking process could also remove tacky contaminants from the treated wastepaper, in order to enhance the quality of deinked paper pulp yielded by the process.